Fin

n. organ attached to various parts of a fish's body (for steering, propulsion, etc.); something which resembles such an organ; five-dollar bill (Slang)

v. remove the fins from a fish; move the fins (pertaining to fish)

FIN may refer tothe ISO 3166-1 alpha-3-code for Finland.a Financial Accounting Standards Board FASB Interpretation Number.Federazione Italiana Nuoto, the Italian Swimming Federation.A FIN packet in the Transmission Control Protocol (TCP).The Internationalist League of Norway (Norwegian: Forbundet Internasjonalen i Noreg)Collar number, aka Force Identification Number, a four-character code used to identify uniformed police officers.
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A fin is a surface used to produce lift and thrust or to steer while traveling in water, air, or other  fluid media. The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices.The foremost use of fins is to ensure the directional stability of an object moving through a fluid such as water or air and may be seen in the use of fletching on arrows and fins at the rear of some missiles, rockets, self-propelled torpedoes, and  kinetic energy penetrators. They are typically "planar" (shaped like small wings), although grid fins are sometimes used in specialized cases.
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Noun
1. the cardinal number that is the sum of four and one
(synonym) five, 5, V, cinque, quint, quintet, fivesome, quintuplet, pentad, Phoebe, Little Phoebe
(hypernym) digit, figure
2. one of a pair of decorations projecting above the rear fenders of an automobile
(synonym) tail fin, tailfin
(hypernym) decoration, ornament, ornamentation
(part-holonym) car, auto, automobile, machine, motorcar
3. one of a set of parallel slats in a door or window to admit air and reject rain
(synonym) louver, louvre
(hypernym) slat, spline
(part-holonym) jalousie
4. a shoe for swimming; the paddle-like front is an aid in swimming (especially underwater)
(synonym) flipper, flippers, fins
(hypernym) shoe
5. a stabilizer that resembles the fins of a fish
(hypernym) stabilizer, stabiliser
(hyponym) vane
(part-holonym) ship
6. organ of locomotion and balance in fishes and some other aquatic animals
(hypernym) extremity, appendage, member
(hyponym) dorsal fin
(part-holonym) fish
(part-meronym) ray
(derivation) break water
Verb
1. equip (a car) with fins
(hypernym) equip, fit, fit out, outfit
(derivation) tail fin, tailfin
2. propel oneself through the water in a finning motion
(hypernym) swim
(classification) water sport, aquatics
3. show the fins above the water while swimming; "The sharks were finning near the surface"
(synonym) break water
(hypernym) swim

adv. finely, delicately, elegantly

adj. thin, fine; sharp; keen, slender; astute, sterling, willowy

n. end; close, finish, termination; stop, point, conclusion; death, fate; demise, aim

n. pureness, cleanness

FIN, Finland, country in northern Europe